1. Field of the Invention
The present invention relates to a method and apparatus for selecting mobile links for establishing communications between respective mobile devices and, more particularly, to a method and apparatus for selecting communications links best suited to current conditions from a number of possible communications links as a mobile link moves into and out of range of other wireless communications devices.
2. Description of Related Art
Communications technologies are becoming pervasive at a fast pace. As many people spend considerable amounts of time in an automobile, it will be increasingly a locus of communication. Today, the communications is either simple one-way communication such as radio reception, or an automobile version of the ubiquitous cellular telephone. It is the object of the present invention to provide more sophisticated data communication based on messaging.
Messaging is a form of communication that is performed on an as-needed basis, meaning that there is no communication unless there is a message. A message is an arbitrary unit of data used to communicate between a sender and a receiver, as well as other participating parties. So, for example, a media server might use messages containing video clips to service a client. Such messages can be used in modern communication systems to carry many types of traffic: voice, video, graphics as well as text messages.
A problem well known to those skilled in the art is the problem of reliable message delivery, where the communication from sender to receiver, or vice versa, must be reliable. This problem is acute in a mobile system such as an automobile, where wireless communication devices are needed to accommodate the mobility inherent in the system. Once committed to wireless, the designer faces the reliability problems inherent in the medium: multipath, noise, signal power, distance from station, and overloaded “cells”. These problems are reasonably common, but have been addressed successfully in the voice domain with a large-scale and costly infrastructure of radio transceivers, coupled to handsets with considerable emissions. Message communications are generally more tolerant of delay, but less tolerant of bit errors.
A variety of methods have been developed to forward messages along a path from a sender to a receiver. These methods are largely store-and-forward, meaning that a message is received, its destination is determined, and it is retained until successfully forwarded towards the destination. This is the basis, for example, of the devices called “routers” in the IP-protocol based networks, which contain both forwarding logic and logic for “routing”, which are addressed next.
Routing is the set of decisions necessary for a set of forwarding actions to transport a packet sent from a source to a destination. One of the attractive features of the pure packet-switching model is its dynamism—the ability to dynamically select a path over which progress towards the destination can be made. In this model, high reliability is achieved by determining, using and constantly updating (at least in principle) a “best path” through the store-and-forward network. In order to cope with packet losses a reliable transport protocol such as TCP/IP is used—TCP/IP provides acknowledgements and retransmissions to ensure reliability in the face of packet loss and corruption. TCP/IP and similar protocols are well-suited to the application area of Autoband, but further problems arise from wireless phenomena, and the mobility of the automobile itself. The invention disclosed here addresses those problems.